Cooking spray
1 (1-pound) boneless sirloin steak
1/2 teaspoon kosher salt, divided
3/8 teaspoon ground black pepper
2 tablespoons unsalted butter
1 1/2 teaspoons grated lemon rind, divided
1 teaspoon fresh lemon juice
1/2 teaspoon anchovy paste
1 teaspoon extra-virgin olive oil
1/4 cup presliced onion
2 garlic cloves, sliced
1/4 teaspoon crushed red pepper
1/2 cup fat-free, lower-sodium chicken broth
8 ounces broccoli rabe (rapini), cut into 1-inch pieces